Electron lens structure



May 13 19 5?. c. H. BACHMAN ELECTRON LENS STRUCTURE Filed May 25, 1944 2 Sheets-Sheet l Fig. l.

Invent o r Charles H. Baohman b 5 Haw 7 Jami-M His Attorney.

y 1947' c H. BACHMAN 2,420,514

ELECTRON LENS STRUCTURE Filed May 25, 1944 2 Sheets-Sheet 2 Inventor: Charles H. Baqhman;

Patented May 13, 1947 ELECTRON LENS STRUCTURE Charles H. Bachman, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application May 25, 1944, Serial No. 537,273

13 Claims. 1

My invention relates to electron lens systems of the electrostatic type and has for its object to provide a new and improved electron lens structure.

In one of the common types of electron lens systems of the electrostatic type a pair of outer electrodes are maintained at the potential of the casing or envelope which encloses the lens and a central electrode is positioned at a high potential with respect to the outer electrodes and the envelope. It is customary to support the central electrode from the envelope by means of insulators. It is an object of the present invention to provide an improved form of electrostatic electron lens in which a central electrode is supported from an outer electrode by means of insulators to take advantage of the axial space available in a lens system for increased insulation and operation of the lens at higher potential.

It is another object of my invention to provide an improved electron lens system in which more accurate alignment of a central electrode with respect to outer electrodes is obtained.

It is a still further object of my invention to provide a new and improved structure for an electrostatic electron lens which permits assembly of the lens as a unitary structure.

One of the features of the invention is the use of an insulator supported on an outer electrode in an electrostatic electron lens system as means to support a centrally disposed. electrode operated at a substantial potential with respect to the outer electrode to permit operation of the central electrode at higher voltages. lator supported on the outer electrode is placed outside of the intense fields of the lens system to avoid electrodeless discharges and leakage across the insulator, as Well as to avoid the abstraction of occluded gases from the insulator body by the intense electric fields.

In another form, the invention employs an insulator which is reentrant in form to provide an increased insulating path between the electrodes of an electron lens.

Th objects and advantages of my invention may best be understood by reference to the fol-- lowing description taken in connection with the accompanying drawing and the features which I desire to protect are pointed out with particularity in the appended claims. In the drawings, Fig. 1 is a sectional view of an electron lens system of the electrostatic type suitably embodying the invention together with a mandrel used in assembling the lens; Fig. 2 is a modification of The insuthe lens system of Fig. 1 in which an increased length of insulation is provided by the electrodes of the system; Fig. 3 shows a further modification of the invention which is particularly adapted for the formation of a unitary electron lens structure; Figs. 4 and 5 show alternative insulator structures suitable for use in conjunction with the outer electrode of an electron lens system to support the insulators outside of the high electric fields of the system; Figs. 6 and 7 are a front elevation and a side view, partly in crosssection, respectively, of another modification of the lens supporting insulators; Figs. 8 and 9 are a front elevation and a side view, partly in crosssection, of another modification of the insulator used in positioning the insulator and the electrodes; and Fig. 19 shows an adjusting means used in connection with the lenses of Figs. 6 and 8.

Referring to Fig. 1, there is shown an electron lens of the electrostatic type, together with a mandrel employed in assembling the lens. The electron lens comprises a pair of outer electrodes 5, 2 in the form of metallic disks each having a central aperture 3 and a pair of additional apertures 4, 5, the purpose of which is pointed out in greater detail later. The electron lens system also includes an intermediate electrode 6 in the form of a metalic disk having a smaller diameter than disks l and 2 and likewise provided with a central aperture 1 larger in size than the apertures 3 in the electrodes I and 2. In the usual electron lens system of the electrostatic type, the electron lens system is enclosed in an envelope Or casing, such as the metallic cylinder 8 and the electrodes I and 2 are in conductive contact with the cylinder 8 so that they are maintained at the potential thereof. The electrodes I and 2 are spaced apart along the tube by means of an annular sleeve 9. In the operation of the electron lens, for example, in an electron microscope, the electrode 5 is maintained at a substantial potential. difference with respect to the electrodes I and 2 so that a beam of electrons, such as the beam it passing longitudinally through the apertures 3, l, is refracted by the lens action of the electrodes. In order that this lens action be as great as possible, it is desirable to maintain the electrode 6 at a very high potential differential with respect to the electrodes l and 2. In structures heretofore used, limitations have been found in insulating means used for supporting the electrode 6 with its aperture in alignment with the apertures of electrodes l and 2.

In order to provide a support for the electrode 6 which permits the use of extremely high potential difference between the electrode 5 and the electrodes I and 2, as well as to permit accurate alignment of the apertures of the electrodes, a cup-shaped insulating member I! is attached to the outer surface of electrode 5, as by means of a plurality of screws I2, and has an outwardly flanged portion I3 provided with a pair of apertures I4 through which pass a pair of threaded rods i5, I6 which are rigidly attached to the electrode 6, as by welding. The insulator may be of any suitable insulating material, for example, a ceramic bonded mica such as Mycalex. Nuts I7 engaging the threads on rods I5, I5 are used to lock the rods to the flange I3 of the insulator. The rod I 5 may be of a length so that it extends only to the electrode 6, while the rod It may be of greater length and may extend to the center electrodes of additional electron lenses employed and to a source of potential.

To assist in aligning the apertures of the electrodes I, 6, as well as to permit accurate spacing of these electrodes, a mandrel I8 may be employed. The mandrel I8 is shown as having two portions I9, 29 of a diameter corresponding to the diameters of the apertures 3, 6 and a pair of shoulders 2I 22 spaced apart by the desired spacing between electrodes I and 6. The holes in the insulator I I through which screws I2 pass, are larger than the body of these screws so that sufficient lateral adjustment is provided to accurately align the apertures of the electrodes. The longitudinal spacing of the electrodes is obtained by adjustment of the side rods I6 and I5 in the insulator and of the nuts II. In actual practice, alignment of the apertures in electrodes I and 6 by means of mandrel I8 is performed of course prior to the insertion of the electrode 2. After electrodes I, 6 are aligned, the mandrel is removed and electrode 2 is placed in the position indicated in Fig. 1 to complete assembly of the lens.

In Fig. 2, there is shown another modification of the insulator used for supporting the electrode B from electrode I in which the insulator 23 is reentrant in form to provide a longer insulating path between the electrode I and the rod I6 at the potential of the central electrode 6.

In Fig. 3, there is shown an electron lens assembly which is in the form of a unitary structure. In this form of the electron lens system, a plurality of stand-oil insulators 24, 25 are seated in suitable recesses 25, 21 in the electrodes I and 2 and the rod I6 connected to the electrode 6 passes through holes in insulators 24, 25. The rods II engaging the threads of the rod I6 permit tightening of the electrodes I, 2 to the spacer 9. Each of the insulators 24, 25 may be provided with reentrant portions 28 which increase the length of the insulating path between the active electrode elements to permit operation of the lens at increased potential diiierences, The electron lens of Fig. 3, which may be assembled as a unit and which may subsequently be inserted into a desired system, avoids the mechanical feats required in installing the parts of an electron lens in the usually crowded spaces of an electron microscope, for example.

Fig. 4 shows an alternative form of an insulator 29 suitable for use in an electron lens system where extremely high potential gradients are desired. The insulator 29 comprises a plurality of reentrant parts 33, 3I which provide a sinuous path between the active electrode parts of the electron lens. Fig. 5 shows another form of insulator which comprises a pair of straps 32, 33 attached to the electrode I. This particular construction gives a greater ratio of insulator path length to width and increases the breakdown voltage of the insulator structure.

Referring now to Figs. 6 and '7 jointly, there is shown another modification of the invention in which there is attached to the outer electrode 2 of an electron lens system a metallic spider 34 having three legs upon each of which is supported an insulating pillar or column 35, the columns being attached to the spider 34 by means of screws 36. Each of the columns 35 is in screwthreaded engagement with a metallic ring member 31 at its end remote from the spider 34, Thus, the members 35 function as three columns supporting the ring 31 from the spider 34. Depending from the ring 3'! are three additional insulating columns 38 which are in alignment with apertures 39-4I in the electrode 2. The central electrode 6 of the electron lens has attached thereto a plurality of metallic rods 42 which project through the apertures 39--4I and pass through holes in the bottom of the insulators 38. Screws 43 in the apertures in insulators 38 serve to clamp the rods 42 and the electrode 6 to the insulator structure. The spider 34 is attached to electrode 2 by means of a plurality of screws 44. A plurality of pusher or looking screws 45 assist in aligning the apertures in electrodes 2 and 6. An enlarged View of the spider attaching and adjusting structure just described is shown in Fig. 10 wherein the spider 34 is shown as having apertures 46 larger than the diameters of the screws 44 so that the spider may be adjusted laterally. In order to prevent th metallic ring 31 which supports the insulators 38 from aifecting the electron stream projected through n electron lens, a shield in the form of a metallic tube 4! is attached to the spider 34 around the central aperture therein and projects longitudinally of the electron lens. This shielding also eliminates spurious deflections and aberrations of the electron beam which may be caused by electrostatic charges built up on the insulator surfaces.

In Figs. 8 and 9 there is shown a modification of the arrangement of Figs. 6 and '7 in which the spider 34 is provided with a, centrally located stud 48 and an annular reentrant insulator 49 is in screw-threaded engagement therewith. The insulator 49 has a flange portion 50 provided with a plurality of apertures 5|. A shoulder on the rods 42 connected to electrode 6 engages cooperating shoulders in the apertures SI and screws 43 serve to clamp the insulator 49 to the rods 42. Each of the screws 43 is provided with a smooth polished metal cap 52 to reduce the possibility of arcing between this end of the electrode supporting rods and any surrounding structure.

In the foregoing ther has been described an improved electrode supporting insulator for an electrostatic electron lens system in which the axial space available between the lens elements is utilized for increasing the insulation of the electrodes and to permit their operation at higher potential differences. Moreover, the insulating surfaces proper are not exposed to the surface charge and leakage effects encountered when the insulators are included between the electrodes of the lens. In addition to permitting operation at higher potentials than those heretofore used, the lens structures shown have the additional advantage that they provide improved line-up of the centers of the electrodes of the-lens system.

While the invention has been described by ref erence to particular embodiments, it will be understood that numerous modifications, may be made by those skilled in the art without actually departing from the invention and I therefore aim to cover in the appended claims all such equivalent variations as fall within. the true spirit and scope of the foregoing description.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrostatic electron lens structure comprising three disk-like electrodes arranged in spaced coaxial alignment and provided with aligned central apertures, means for supporting an outer one of said electrodes, the intermediate of said electrodes being supported by and insulated from said outer one of said electrodes.

2. An electrostatic electron lens structure comprising two disk-line electrodes arranged in spaced coaxial alignment and provided with central apertures, means for supporting one of said electrodes, and means for insulatingly supporting the other of said electrodes solely from said one electrode and for aligning said apertures.

3. An electrostatic electron lens structure comprising three disk-like electrodes arranged in spaced coaxial alignment and provided with aligned central apertures, and means for insulatingly supporting the intermediate of said electrodes from the surface of an outer one of said electrodes remote from said intermediate electrode.

4. An electron lens comprising a pair of metallic disks having aligned centrally positioned apertures, an insulator attached to the surface of one of said disks remote from the other of said disks and extending in a direction transverse to said apertures, and a conductive member attached to said other disk at a point spaced from said aperture and extending in a direction transverse to said disks, said member and said second disk being supported from said insulator.

5. An electron lens comprising a pair of metallic disks having aligned centrally positioned apertures, an insulator attached to the surface of one of said disks remote from the other of said disks and extending in a direction transverse to said apertures, and a conductive member attached to said other disk at a point spaced from said aperture and extending in a direction transverse to said disks, said member having a length greater than the distance between said disks, and said member and said second disk being supported from said insulator.

6. An electron lens comprising a pair of metallic disks having aligned centrally positioned aptures, an insulator attached to the surface of one of said disks remote from the other of said disks and extending in a direction transverse to said apertures, and a conductive member attached to said other disk at a point spaced from said aperture and extending in a direction transverse to said disks, said member and said second disk being supported from said insulator and said insulator being reentrant in cross sectional configuration to increase the length of the insulating path between said surface and said member.

7. An electron lens comprising a pair of metallic disks having centrally aligned apertures, the first of said disks having an additional aperture, an insulator attached to the surface of said first disk remote from the other of said disks and extending in a transverse direction overlying said additional aperture, and a conductive member rigidly connected to said second disk and passing through said additional aperture, said other disk and said conductive member both being supported from said insulator.

8. An electron lens comprising a pair of disklike electrodes each having a central aperture therein, an additional disk-like electrode positioned between said pair of electrodes and having an aperture in alignment with the central aperture of said pair of electrodes, and means for insulatingly supporting said additional electrode from the remote surface of one of said pair of electrodes comprising a reentrant insulator attached to said surface, said one electrode having a second aperture spaced radially from said central aperture and said insulator having a transversely extending flange overlying said second aperture, and a conductive rod rigidly connected to said additional electrode and projecting through said second aperture supported from said flange.

9. A unitary electron lens comprising a pair of disk-like electrodes separated by a tubular spacer, an additional electrode positioned between said pair of electrodes, each of said electrodes having centrally aligned apertures, each of said pair of electrodes having additional aligned apertures spaced radially from said central apertures, and means for supporting said additional electrode and for rigidly connecting said pair of electrodes and said spacer comprising a pair of insulators engaging respectively the surface of each of said pair of electrodes remote from said additional electrode and overlying said additional apertures, and a conductive member rigidly attached to said additional electrode and supported by said insulators.

10. In an electron lens of the electrostatic type, the combination of a pair of disk-like electrodes having aligned centrally located apertures, and means for insulatingly supporting one of said electrodes from the other of said electrodes comprising a spider attached to the surface of said other electrode remote from said one electrode, insulating means supported from said spider, and conductive means supported from said insulator and rigidly attached to said one electrode.

11. In an electron lens of the eelctrostatic type, the combination of a pair of disk-like electrodes having aligned centrally located apertures, and means for insulatingly supporting one of said electrodes from the other of said electrodes comprising a spider attached to the surface of said other electrode remote from said one electrode, insulating means supported from said spider, conductive means supported from said insulator and rigidly attached to said one electrode, and means for adjusting the lateral position of said spider to align said apertures.

12. In an electron lens system of the electrostatic type, the combination of a pair of disklike electrodes having centrally aligned apertures, and means for insulatingly supporting one of said electrodes from the other complrising a movable member adjustably attached to the side of said other electrode remote from said one electrode, insulating means supported on said movable member, and rigid means connected between said insulating means and said one electrode.

13. In an electron lens system of the electrostatic type, the combination of a pair of disk like electrodes having centrally aligned apertures through which an electron beam is projected, and means for insulatingly supporting one of said electrodes from the other comprising a movable member adjustably attached to the side of NIT AT P ENT said other electrode remote from said one elec- Number Name Date trode, insulatin means supported on said mov- 2,248 558 Schlesinger July 8, 1941 able member, rigid means connected between said 5 2 296:1O2 Gray Sept 15, 1942 insulating means and said one electrode, and 2260351 Bruche 1941 shielding means positioned between said beam and 267,083 De G181. 1941 Said insulator- 2,161,316 Rogowaki et al. June 6, 1932 CHARLES BACHMAN- 2,163,740 Wales, Jr. June 27, 1939 2,084,364 Zworykin June 22, 1937 REFERENCES CITED The following references are of record in the file of this patent: 

